1. Field of the Invention.
This invention relates to fluid-operated actuators generally and, more particularly, to a novel fluid-operated actuator which combines a relatively long actuating stroke with force multiplication.
2. Background Art.
While the present invention is described as being applied to the actuation of workpiece engagement means such as collets, vises, and chucks on machine tools and the like, it will be understood that it may be applied as well in any case where it is desired to provide a relatively long actuating stroke with force multiplication. Conventional chucks, collets, and actuators of the types described here are manufactured, for example, by Powerhold, Inc., Middlefield, Conn.
Collets and chucks on automatic lathes were originally moved between their open and clamped positions by linear motion provided by pneumatically-operated pistons which were supplied by pressurized air available in manufacturing plants, typically on the order of 80-85 pounds-per-square-inch pressure. The pistons provide movement of the clamping mechanism into contact with the workpiece and then provide the clamping force to grasp the workpiece. Relatively low force is required to move the clamping mechanism into contact with the workpiece, but it is usually desirable that relatively strong force be available for grasping the workpiece. Since the force developed by such a piston is equal to the product of the pressure of the air times the area of the piston, requirements for higher clamping forces required the use of larger diameter piston cylinders or the use of higher pressure air, if available. The larger diameters had practical and economical limits, so, eventually, hydraulically-actuated pistons came into use for applications requiring high clamping forces, with hydraulic units easily providing pressures of 1000 pounds per square inch or higher. That necessitated adding the relatively high cost of a hydraulic unit, but the same unit could also be used for actuating auxiliary attachments, such as tail stock aligners. That multiple use of the hydraulic unit helped spread its cost over a number of items.
Now that most such machines have their auxiliary attachments electrically actuated by computer control, it is necessary, in some cases, to provide a hydraulic unit solely for the actuation of the clamping mechanism, which means that the overall cost of the clamping mechanism is relatively high. It would thus be desirable to have a pneumatically-operated actuator of relatively small size that could produce the higher clamping pressures required.
While there are a number of mechanical devices known in the art which may be employed to multiply force, none is able to conveniently provide the relatively long linear stroke that is required to actuate such clamping mechanisms, which long stroke is easily provided by a piston.
Accordingly, it is a principal object of the present invention to provide a fluid-operated actuator that can provide a relatively large force when powered with compressed air.
A further object of the present invention is to provide such an actuator which can provide force multiplication combined with a relatively long linear stroke.
An additional object of the present invention is to provide such an actuator that is relatively small in diameter.
Other objects of the present invention, as well as particular features and advantages thereof, will, in part, be apparent and will, in part, be obvious from the following description and the accompanying drawing figures.